Heretofore, an easy-to-open packing bag having the following construction as shown in FIG. 6 is used to pack an elongated flat article such as a blood sugar value measuring electrode therein. Surfaces of thermoplastic resinous layers of two rectangular packing films each consisting of a backing layer and a thermoplastic resinous layer are laminated on each other. One of the shorter sides of each packing film is formed as a non-bonding portion 15. A separable U-shaped peripheral heat-bonding portion 12 is formed along the other three sides of each packing film. A separable mountain-shaped projected heat-bonding portion 13 connecting both ends of the peripheral heat-bonding portion 12 with each other and projected outward is formed and sealed. A pair of confronting partitioning heat-bonding portions 14 projecting inward is formed to the peripheral heat-bonding portion 12 to accommodate a content 7 such as the blood sugar value measuring electrode in a space positioned at one side and a drying agent 8 in a space positioned at the other side. When the packing bag having the above-described construction is used to accommodate the blood sugar value measuring electrode therein, the external and internal packing films of the non-bonding portion 15 are picked up with fingers and pulled in opposite directions, and then, both projected heat-bonding portions 13 are separated from each other from ends thereof to a tearing line 16. Then, the separated portions of the packing films are bent outward to expose an end of the blood sugar value measuring electrode to the outside from the easy-to-open packing bag. Then, the exposed portion is impregnated with blood to measure a blood sugar value. However, the area of the nonbonding portion 15 is not large and thus it is not easy to pick up the non-bonding portion 15. Further, a strong force is required to separate the entire heat-bonding portions 13 from each other from the ends thereof. Thus, if an excess force is applied to the packing films to open the easy-to-open packing bag, the entire packing films separate from each other and the blood sugar value measuring electrode drops from the easy-to-open packing bag. Thus, it is difficult for old men who have to use the blood sugar value measuring electrode frequently to open the easy-to-open packing bag.